Yogurt-Lover Wiki
Welcome to the Yogurt-Lover Wiki Yogurt lovers gather here to learn about your favorite snack! Find information on how yogurt is made, the biochemistry behind yogurt making, yogurt's health benefits and much much more! Written by: Andrew Lee, Sojung Lee, Sai Chalasani, Dayoung Rowen Moon, Susie Son, Olivia Byun What is Yogurt? The Food and Agriculture Organization of the United Nations defines yogurt as "the coagulated milk product obtained by lactic acid fermentation through the action of Lactobacillus delbrueckii ''ssp. ''bulgaricus (L.bulgaricus) ''and ''Streptococcus thermophilus (Strep. thermophilus) ''from milk and milk products" with the result of an abundant and viable amount of microorganisms in the final product.1 Modern yogurt has branched out into a sea of different varieties ranging from the more eclectic frozen yogurt and yogurt beverages to more traditional types of set and stirred yogurts. It has become a very popular snack in industrialized countries with global sales of yogurt amounting to approximately $40 billion US dollars in 2006.1 Dairy interesting, tell me more! Yogurt Manufacturing First, milk is blended with milk powder to standardize the fat and protein content of the milk to an optimum level.2 Sometimes, stabilizers are added to enhance the properties of yogurt, such as texture or appearance. Then, homogenization of milk is performed by the use of pressure. This prevents fat separation in the yogurt during storage. The homogenized milk is then heated to get rid of unwanted microorganisms and dissolved oxygen (DO) to facilitate growth of starter cultures. The starter cultures are then added after the milk has been cooled to the incubation temperature. During the growth of the starter cultures, lactose is converted into lactic acid, lowering the pH of the yogurt. When an optimum pH is reached, the yogurt products are cooled and packaged. To ensure that the yogurt is properly made and suitable for consumers, sensory evaluations are usualy carried out.2 Sensory evaluations are the testing of products by panelists to ensure that the product is suitable for its customers. For example, a typical evaluation involves each panelist ranking the smoothness, sourness, and mildness of yogurt. This is an essential step in yogurt manufacturing as the sensory evaluation is crucial to test the salability of the final product. It exposes the viewpoint of multiple subjects and evaluates it to see if it will be a suitable product for consumers. That Yogurty Taste... Looking to make that perfect yogurty goodness? The answer is quite simple - regulation. During the process of manufacturing yogurt, various factors, such as temperature and dissolved oxygen (DO) levels, are regulated in order to produce the "best". One of these factors also includes lactate (lactic acid) concentration. It may not have a direct effect on its quality; however, it is a precursor to many.3 For example, lactate is responsible for the production of acetaldehyde, which gives rise to the distinct flavour in yogurt. By extrapolating this information, it can be assumed that greater concentrations of lactate can produce more acetaldehyde and thus, create a more distinct flavour. Not only that, lactate concentration is also used to determine when the yogurt is ready.2 This is supported by the fact that greater lactate concentration decreases pH, which in turn increases acidity where a desired 0.7% acidity is reached when fermentation is complete (Figure 1). The presented data demonstrates its relevance by proving that fermenation is terminated at 0.7% acidity by comparing two different methods, LT-ROF (with previous sterile nitrogen gas treatment) and control fermentation (without previous treatment). As published in the figure, it took 180 min to fully ferment using LT-ROF and 210 min using control fermentation. This also manifests the efficiency of LT-ROF above control fermentation. Lactate concentration is also related to curd thickness/firmness in that when the two yogurt starter cultures interact with milk to form curd, lactate is a byproduct. With this, it can be interpreted that with a greater concentration of lactate, greater thickness/firmness of curd can be expected.4 The variables influencing taste of yogurt are directly affected by the incubation conditions of the starter culture. Recently, a method for creating superior set yogurt with a smoother texture was found that involved lower temperatures of incubation and zero dissolved oxygen content (DO content). Yogurt: brought to you by ''Streptococcus ''and Lactobacillus! ''S. thermophilus and L. bulgaricus are the lactic acid bacteria used most widely in yogurt production.7 They are both facultative anaerobic bacteria which means they can switch between aerobic (presence of oxygen) and anaerobic (no oxygen) types of metabolism.2,5 Under anaerobic conditions, they grow by fermentation or anaerobic respiration, but in oxygenated environments, they switch to aerobic respiration. The optimum temperature of these organisms is 40-45°C and the desired pH is around 4.6. At this optimum temperature and pH, yogurt has a desired firmness in its curds and a fast rate of acid production. The firmness of yogurt is important to maintain its structure during transportation and directly impacts the salability of the yogurt.1 Both bacteria S. thermophilus ''and ''L. bulgaricus produce lactic acid at a great rate.6 These two bacteria grow symbiotically through a process known as proto-cooperation.7 This association results in increased growth of both bacteria, increased acid production, higher aromatic compound production (aromatic compounds are responsible for the aroma of yogurt), and most importantly, increased overall yield of fermentation. Each bacterium is advantageous for the growth of the other. For example,'' S. thermophilus stimulates the growth of ''L. bulgaricus ''through its anaerobic production of formic acid and carbon dioxide. The production of carbon dioxide is unique to ''S. thermophilus ''in lactic acid bacteria, which catalyzes the decarboxylation of urea with urease. In return, ''L. bulgaricus ''releases animo acids through its degradation of casein, something that most strains of ''S. thermophilus are incapable of. The amino acids released accelerate the growth of'' 'S. thermophilus.'' What goes on Behind the Scenes! References (1) W. J. Lee, J.A. Lucey. Formation and physical properties of yogurt. ''Asian-Aust. J. Anim. Sci. ''2010'. 23 (9): 1127-1136. (2) Horiuchi, H., Inoue, N., Liu, E., Fukui, M., Sasaki, Y., Sasaki, T. A method for manufacturing superior set yogurt under reduced oxygen conditions. J. Dairy Sci. 2009. 92: 4112-4121. (3) Hamdan, I.Y., Kunsman Jr, J.E., Deanne, D.D. Acetaldehyde production by combined yogurt cultures. J. Dairy Sci. 1971, 54(7): 1080-1082. (4) Ramchandram, L. Physico-chemical and therapeutic properties of low-fat yogurt as influenced by fat replacers, exopolysaccharides and probiotics. VUIR. 2009: 23-25. (5) C. T. Grey., J. W. Wimpenny., M. R. Mossman.Regulation of metabolism in facultative bacteria: II. Effects of aerobiosis, anaerbiosis and nutrition on the formation of Krebs cycle enzymes in escherchia coli. BBA-GEN SUBJECTS. 1966. 117: 33-41. (6) P.A. Shankarand., F.L. Davies. associative bacterial growth in yogurt starters; initial observations on stimulatory factors. INT J DAIRY TECHNOL. 1997. 30: 31-32. (7) Herve-Jimenez, L.; Guillouard, I.; Guedon, E.; Boudebbouze, E.; Hols, P.; Monnet, V. Maguin, E.; Rul, F. Postgenomic Analysis of Streptococcus thermophilus Cocultivated in Milk with Lactobacillus delbrueckii subsp. bulgaricus: Involvement of Nitrogen, Purine, and Iron Metabolism. ''AEM. '2009. '''75(7):2062-2073. (8) Zourari, A., Accolas, JP., Desmazeaud, MJ. Metabolism and biochemical characteristics or yogurt bacteria. A review. ''Lait. 1992. 71: 1-34. (9) Desobry-Banon, S., Hardy, J., Vetier, N. health benefits of yogurt consumption A review. International journal of Food properties. 2009, 2 (1): 1-12. (10)MacDonald, M. September 17 ATP and glycolysis Notes. McMaster University, Hamilton, ON. 2013. Category:AWefawef Category:Browse